For processing a large number of papers, a commercially available office machine (e.g. a scanner, a printer or a multifunction peripheral) is usually equipped with an automatic document feeder. By means of the automatic document feeder, a stack of papers can be successively fed into the office machine in order to perform the scanning task or the printing task. However, if the paper is not placed at the proper position or if the paper is aslant fed into the automatic document feeder, the printed or scanned image is skewed. For solving these drawbacks, the automatic document feeder usually has a special device for correcting the skewed paper before the paper is introduced to the working region (e.g. the scanning region or the printing region) in order to decrease the skew degree of the printed or scanned image.
In accordance with the conventional approaches of correcting the skewed paper, the rotation of a transmission roller is selectively stopped or reversed during the process of feeding the paper. Hereinafter, the approaches of correcting the skewed paper by stopping the transmission roller will be illustrated with reference to FIGS. 1A, 1B and 1C. FIG. 1A is a schematic side view illustrating a conventional paper deskew device during the paper-feeding task is performed. FIG. 1B is a schematic side view illustrating the conventional paper deskew device of FIG. 1A during the deskew task is performed. FIG. 1C is a schematic side view illustrating the conventional paper deskew device of FIG. 1A after the paper-feeding task is performed.
As shown in FIG. 1A, the conventional paper deskew device 1 comprises a feed roller 11, a transfer roller 12, and a transmission roller 13.
When the paper-feeding task starts, the feed roller 11 and the transfer roller 12 are rotated in a first direction “a” to feed a paper 14 into the office machine. Under this circumstance, the transmission roller 13 is in a static status. If the paper 14 is not skewed, the both sides of the front edge of the paper 14 are simultaneously contacted with the transmission roller 13. On the other hand, if the paper is skewed, a side of the front edge of the paper 14 is firstly contacted with the transmission roller 13. Meanwhile, the paper 14 is blocked by the transmission roller 13 from being continuously advanced. Since the paper 14 is continuously transported by the transfer roller 12, the front edge of the paper 14 is slightly upturned (see FIG. 1B). Until the other side of the front edge of the paper 14 is moved to the transmission roller 13, the both sides of the front edge of the paper 14 are both contacted with the transmission roller 13. Meanwhile, the paper 14 is not continuously advanced, and thus the purpose of correcting the skewed paper is achieved.
After the skewed paper has been corrected, the transmission roller 13 is rotated in the first direction “a” (see FIG. 1C) to feed the paper 14 into the office machine.
Hereinafter, the approaches of correcting the skewed paper by reversing the transmission roller will be illustrated with reference to FIGS. 2A, 2B and 2C. FIG. 2A is a schematic side view illustrating another conventional paper deskew device during the paper-feeding task is performed. FIG. 2B is a schematic side view illustrating the conventional paper deskew device of FIG. 2A during the deskew task is performed. FIG. 2C is a schematic side view illustrating the conventional paper deskew device of FIG. 2A after the paper-feeding task is performed.
As shown in FIG. 2A, the conventional paper deskew device 2 comprises a feed roller 21, a transfer roller 22, and a transmission roller 23.
Except for the following items, the operations of the paper deskew device 2 are substantially identical to those of the paper deskew device 1. In contrast, after the paper 24 has been transported across the transfer roller 22 for a certain time period, the transmission roller 23 is rotated in a second direction “b” (see FIG. 2B) from the original static status. Meanwhile, the paper 24 is blocked by the transmission roller 23 from being continuously advanced. Since the paper 24 is continuously transported by the transfer roller 22, the front edge of the paper 24 is slightly upturned. Until the other side of the front edge of the paper 24 is moved to the transmission roller 23, the both sides of the front edge of the paper 24 are both contacted with the transmission roller 23, so that the purpose of correcting the skewed paper is achieved.
After the skewed paper has been corrected, the transmission roller 23 is rotated in the first direction “a” (see FIG. 2C) to feed the paper 24 into the office machine.
The above conventional paper deskew devices, however, still have some drawbacks. For example, it takes an additional time period for allowing the motor to drive start-up of the transmission roller from the static status. Moreover, it also takes another time period to change the driving direction of the motor. In other words, the time period for performing the scanning or printing task will be increased. Since the driving direction of the motor is frequently changed or the motor is frequently started from the static status, the possibility of causing damage of the motor will be increased. Under this circumstance, the use life of the automatic document feeder will be shortened.
Therefore, there is a need of providing an improved paper deskew device for correcting the skewed paper.